As the above power supplying system, for example, the systems shown in FIGS. 21 and 22 are known (PTL1, PTL2). As shown in FIGS. 21 and 22, a power supplying system 1 includes: a power supplying section 3; and a power receiving section 5. The power supplying section 3 is provided with a power supplying loop antenna 6 to which the electric power is supplied, and a power supplying helical coil 7 (power supplying coil) arranged opposite to the power supplying loop antenna 6 with a gap in an axial direction of the power supplying loop antenna 6 and electromagnetically bonded to the power supplying loop antenna 6. When the electric power is supplied to the power supplying loop antenna 6, the electric power is transmitted to the power supplying helical coil 7 by electromagnetic induction.
The power receiving section 5 is provided with a power receiving helical coil 8 (power receiving coil) arranged opposite to the power supplying helical coil 7 with a gap in an axial direction of the power supplying helical coil 7 and electromagnetically resonating with the power supplying helical coil 7, and a power receiving loop antenna 9 arranged opposite to the power receiving helical coil 8 with a gap in an axial direction of the power receiving helical coil 8 and electromagnetically coupled to the power receiving helical coil 8. When the electric power is transmitted to the power supplying helical coil 7, the electric power is transmitted to the power receiving helical coil 8 wirelessly by electromagnetic resonance.
Further, when the electric power is transmitted to the power receiving helical coil 8, the electric power is transmitted to the power receiving loop antenna 9 by electromagnetic resonance, and supplied to a load connected to the power receiving loop antenna 9. According to the above power supplying system 1, the electric power can be transmitted from the supplying side to the receiving side wirelessly by the electromagnetic resonance between the power supplying helical coil 7 and the power receiving helical coil 8.
Further, when the power receiving section 5 is provided on a vehicle 4, and the power supplying section 3 is provided on a road 2 or the like, it is considered that the electric power is supplied to the load mounted on the vehicle 4 wirelessly using the power supplying system 1. Incidentally, in the power supplying system 1, it is difficult to stop the vehicle in a manner that a central axis C1 of the power supplying helical coil 7 and a central axis C2 of the power receiving helical coil 8 are coaxial, and as shown in FIG. 23, a gap d may be generated between the central axes C1 and C2.
The present inventors simulated the transmission efficiency of the power receiving loop antenna 9 of a conventional product A as the power supplying system 1 shown in FIG. 22 when the gap d between the central axes C1 and C2 is varied within a range from 0 mm to D mm. The result is shown by solid line in FIG. 24.
Incidentally, in this case, the power supplying loop antenna 6 and the power receiving loop antenna 9 are the same, and a diameter R11=R12=0.6D mm. The power supplying helical coil 7 and the power receiving helical coil 8 are the same, and a diameter R21=R22=D mm. Further, a distance L1 between the power supplying helical coil 7 and the power receiving helical coil 8 is fixed to 0.68D mm. Further, the characteristic impedances of both power supplying loop antenna 6 and the power receiving loop antenna 9 are 50Ω.
As shown by solid line in FIG. 24, when the gap d between the central axes C1, C2 is 0 mm to 0.33D mm, the transmission efficiency is almost 100%. When the gap d between the central axes C1, C2 is more than 0.33D mm, the transmission efficiency starts to reduce. As the gap d becomes larger, the reduction of the transmission efficiency becomes larger.
Therefore, for solving this problem, as shown in FIG. 25, it is considered that the diameter R21 of the power supplying helical coil 7 is larger than the diameter R22 of the power receiving helical coil 8 to suppress the reduction of the transmission efficiency.
In a conventional product B as the power supplying system 1 shown in FIG. 25, a measurement result of the transmission efficiency of the power receiving loop antenna 9 when the gap d between the central axes C1, C2 is varied in a range from 0 mm to D mm is shown by dotted line in FIG. 24.
Incidentally, in this case, the power receiving loop antenna 9 is the same as the conventional product A, and the diameter R12=0.6D mm. The power receiving helical coil 8 is the same as the conventional product A, and the diameter R22=D mm. Further, the diameter R11 of the power supplying loop antenna 6=1.7D mm, and the diameter R21 of the power supplying helical coil 7=2D mm. Further, the distance L1 is fixed to 0.68D mm similar to the conventional product A.
As shown by dotted line in FIG. 24, when the diameter R21 of the power supplying helical coil 7 is larger than the diameter R22 of the power receiving helical coil 8, the reduction of the transmission efficiency is suppressed. In addition, when the diameter R21 of the power supplying helical coil 7 is larger from 2D mm to 4D mm, it was checked that the reduction of the transmission efficiency is further suppressed.
However, there is a problem that even when the diameter R21 of the power supplying helical coil 7 is larger than the diameter R22 of the power receiving helical coil 8, the reduction of the transmission efficiency is not fully suppressed.
Further, the present inventors simulated the transmission efficiency of the power receiving loop antenna 9 of the power supplying system 1 shown in FIG. 25, when the gaps (dx, dy) of the central axes C1, C2 of the power receiving helical coil 8 on an X-Y plane in FIG. 25 are varied in a range 0 mm≦dx≦1.5d1 mm, 0 mm≦dy≦1.5d1 mm. The result is shown in FIG. 26.
Incidentally, in this case, the diameter R12 of the power receiving loop antenna 9 is 0.5d1 mm, and the diameter R22 of the power receiving helical coil 8 is d1 mm. Further, the diameter R11 of the power supplying loop antenna 6 is 2.67d1 mm, and the diameter R21 of the power supplying helical coil 7 is 3d1 mm. Namely, the diameter R21 of the power supplying helical coil 7 is about three times the diameter R22 of the power receiving helical coil 8. Further, the distance L1 between the power supplying helical coil 7 and the power receiving helical coil 8 is fixed to 0.67d1 mm. The characteristic impedances of both power supplying loop antenna 6 and the power receiving loop antenna 9 are 50Ω.
As shown in FIG. 26, when the gaps dx, dy of the central axes C1, C2 are 0 mm to d1 mm, the transmission efficiency is nearly 100%. However, there is a problem that when the gaps dx, dy of the central axes C1, C2 becomes more than d1 mm, the transmission efficiency becomes reduced, and as the gaps dx, dy are larger, the transmission efficiency are further reduced.
Further, in PTL 3, a power supplying system in which a plurality of power supplying coils is arranged in a travel direction of a vehicle is proposed. In this power supplying system, the vehicle is moved in the travel direction by supplying the electric power to the vehicle sequentially with from a rear side coil to a front side coil. The electric power cannot be supplied while the vehicle is stopped.